Another way to make use of mummies, which admittedly may be too weird. The idea was that the gods possess a body to take mortal form, and mummies are easy to possess. Now that I've written this all, it sounds rather silly, but maybe it'll spark some other ideas.

Spirit of Ra 3WW
Enchantment - Aura (U)
Enchant creature.
~ costs 3 less to cast if it targets a mummy.
Enchanted creature is a 4/4 with flying and no other abilities.

"Mummify" would be a great word to use. I'm still not sold on exiling the creature, despite it being a thematic fit, unless there's a mechanical justification (like black spends creatures from your graveyard as fuel).

Maybe we can do something like persist?

Mummify target creature (If it dies with no -1/-1 counters on it this turn, return it to the battlefield with a -1/-1 counter.)

I'm not sure about the identity of Mummies as ability-less creatures. That fits my idea of regular Zombies, but with Mummies I tend to think of them as being powerful, advanced forms of undead rather than a lowly Zombie or Skeleton. I imagine them being as powerful as Vampire lords, some of them as powerful as Liches. But maybe that's just me. Maybe only the Pharaoh-mummies need to be that strong.

I feel that Mummies would be easier to balance if the mummification didn't happen immediately and automatically. It could be an ability that you activate from the graveyard that you had to pay a cost for (such as a mana cost or a discard cost) or satisfy some condition for.

Most mummy stories I've seen cast the mummy as a single powerful Lich-like boss monster. Not all do. Even if they did, Magic puts its on spin on everything, so that'd be okay (provided we make it awesome). The question is, which can we do better? And how much do we need? If we want mummies (plural), mummify is probably our best bet. If we're okay with just one mummy, we can reprint or iterate off of Vengeful Pharaoh.

I don't know what the answer is, and I doubt we'll know before a month's worth of Design. That said, mummify is a neat enough mechanic that I would start there, with the fall-back plan of Vengeful Pharaoh in mind. I mean, chances are we'll discover something different and better than both options, right?

Wouldn't it help having effects triggered off cards exiling (i.e. "where X is the number of exile carss you own" or "whenever a card is exiled")? My original afterlife (maybe minus the obligatory exile) would work well with this mummify (which would provide exile to the battlefield, whereas Pillage did it for the other zones).

I really liked the use of Unearth with "when exiled" triggers. It felt like a creature died, then its restless preserved corpse came back, but soon found eternal peace (in exile). To me that evoked Egyptian preservation of the dead, and afterlife.

Counting exiled cards may pose a problem - there are many cards like Arc Slogger or Doomsday, where the cards are balanced because they exile a whole chunk of your library as a drawback. These cards can easily put like 40 or more cards into exile. Cards that grant bonuses based on the number of exiled cards would be too strong.

While we can carefully design exile-counting cards to avoid overpowered combos with these mass-exile cards, it would still leave a permanent design restriction for the future. Design would lose "massive exile" as a balancing tool for future cards.